Functions, loops and conditional statements

ANU BDSI
workshop Introduction to R programming

Emi Tanaka

Biological Data Science Institute

3rd April 2024

Current learning objective

-Conduct elementary arithmetic operations using R
-Navigate the RStudio interactive development environment (IDE)
-Install external packages in R to extend functionality
-Comprehend various object types in R
-Manipulate lists, matrices, and vectors in R
-Compute basic summary statistics including mean, median, quartiles, and standard deviation using R
-Grasp the concept of missing values within the R environment
-Import and export data in R
Create basic functions, employ conditional statements, and utilize for loops in R
Decipher error messages and do basic troubleshooting

Functions

A function in R has three parts:
- formals(): the list of input arguments,
- body(): the code inside the function,
- environment(): the environment (out of scope for this workshop).
Writing your own functions can make repetitive tasks easier.
You can make a new function using function().

Examining functions

Writing the name of the function without arguments shows the internal code:

Loops

Conditional statements

The condition in the if statement needs to evaluate to a single TRUE or FALSE
ifelse() is the vectorised

Equalty statements

==
%in%

Example

Basic troubleshooting

If you encounter an error,

Read the error message!
Google the error message
Ask for help with a reproducible example

🆘 Asking for help

What do you think about the question below?

🆘 Asking for help 1 Part 2

What do you think now?

I am looking to adjust the size of two separate ggplots within the same R chunk in Rmarkdown. These plots must be different when outputted as a pdf, so defining the dimensions at the beginning of the chunk doesn’t work. Does anyone have any ideas? My code is below.

```{r, fig.height = 3, fig.width = 3}
ggplot(df, aes(weight, height)) +
  geom_point()

ggplot(df, aes(height, volume)) +
  geom_point()
```

🆘 Asking for help 1 Part 3

Is this better?

```{r, fig.height = 3, fig.width = 3}
library(ggplot2)
ggplot(df, aes(weight, height)) +
  geom_point()

ggplot(df, aes(height, volume)) +
  geom_point()
```

🆘 Asking for help 1 Part 4

Okay better now?

```{r, fig.height = 3, fig.width = 3}
library(ggplot2)
df <- read.csv("mydata.csv")
ggplot(df, aes(weight, height)) +
  geom_point()

ggplot(df, aes(height, volume)) +
  geom_point()
```

🆘 Asking for help 1 Part 5

Are we done now?

```{r, fig.height = 3, fig.width = 3}
library(ggplot2)
ggplot(trees, aes(Girth, Height)) +
  geom_point()

ggplot(trees, aes(Height, Volume)) +
  geom_point()
```

❓ How to ask questions?

Checklist (note: not an exhaustive checklist)

Is the problem clearly and succinctly described? Is the expected solution or behaviour outlined? Are you asking the right people at the right place?

If the question is asked in an public forum or similar:

Can people who can answer your question find your question? E.g. does the post have appropriate tags or keywords to reach the right experts?

If the problem is computer system related…

Can the problem be easily reproduced on other people’s system? Is the minimum reproducible code or steps supplied?

If the problem is based on data …

Is the data supplied? If the data is big, could you cull your data further to communicate or reproduce the problem?

🆘 Asking for help 1 Check

Is the problem clearly and succintly defined? Is the expected solution or behaviour outlined? Is the problem asked at the right place or person?

Can people who can answer your question find your question?